KR100656385B1 - Real-time sensor line protocol - Google Patents

Abstract

A communication method of a real-time wireless sensor network having a linear structure is provided to supply a protocol for the sensor network having very low network delay through synchronization between nodes and supply a low-power protocol for the sensor network by minimizing an idle listening time of an active section, thereby reducing power consumption of each node of the sensor network and reliably transmitting data with low transmission delay. In a method for configuring a network of a sensor network for collecting sensing data from plural sensors, the method comprises the following steps of: linearly arranging communication paths of each node so that all sensor nodes except synch nodes and terminal nodes can have one predecessor and one successor; and making nodes, included in the sensor network, perform time synchronization of the entire networks by performing time synchronization of themselves based on operation sections of their predecessors.

Description

Real-time wireless sensor network communication method with linear structure {Real-time Sensor Line Protocol}

1 is a conceptual diagram illustrating a distributed TDMA structure according to the present invention.

2 is a timing synchronization timing diagram according to the present invention;

3 is a conceptual diagram illustrating a time synchronized forwarding mechanism in accordance with the present invention.

4 is a diagram for explaining a virtual communication line configuration process according to the present invention.

5 is a diagram for explaining a virtual communication line reconfiguration process according to the present invention.

6 is a schematic diagram showing a data packet structure according to the present invention;

7 illustrates a buffer structure for priority processing according to the present invention.

The present invention relates to sensor networks, and more particularly to a communication protocol between sensor nodes.

The sensor network is a core technical infrastructure for realizing ubiquitous computing technology and can be operated by wired or wireless connection. In a sensor network, each node uses a limited amount of batteries, so sensing data with the least amount of energy is a top priority. In addition, in order to apply the sensor network to the real-time emergency service, network delay should be minimized in the large sensor network. Therefore, sensor networks that require real-time monitoring require protocols with very low network support while minimizing battery drain.

Nodes of a wireless sensor network operate using batteries with limited sensing, computing, and wireless communications. When applying traditional MAC protocols such as MANET and IEEE802.11 to the sensor network, packet collision, overhearing, control packet overhead, which wastes energy in the wireless network, Problems such as idle listening will occur. In particular, idle listening causes a lot of energy consumption as the sensor node always operates in the active state even when communication function is not required. In order to make up for this drawback, the MAC protocol used in the sensor network saves energy through the method of waking up periodically and operating in the active state while minimizing power consumption by operating in the sleep state. The sensor MAC protocol using this method is as follows.

<Sensor-MAC (S-MAC)>

The S-MAC protocol allows the sensor node to periodically go to sleep mode using a low duty cycle (duty cycle) to reduce idle listening, the biggest energy waster in wireless networks. This operation saves energy, the main purpose of the sensor network, and avoids contention and packet collisions using contention-based scheduling. However, there is a disadvantage in that network delay is increased due to idle listening.

<Timeout-MAC (T-MAC)>

T-MAC is a MAC protocol for contention-based wireless sensor networks such as S-MAC. Energy saving is achieved by applying the active / sleep duty cycle proposed in S-MAC. However, the duty cycle proposed by S-MAC has a characteristic that the energy saving efficiency decreases with the change of traffic environment as it is applied in a fixed form. To compensate for these drawbacks, T-MAC allows the active period to operate flexibly according to the data traffic. This flexible duty cycle allows the T-MAC to further reduce idle listening, increasing energy savings in response to changes in traffic conditions. However, as with S-MAC, there is still a problem of increased network latency due to idle listening.

 <B-MAC>

B-MAC is basically a MAC protocol based on CSMA. This protocol uses low-power listening (LPL) to minimize idle listening. A node that performs listening for a very short time periodically using LPL and sends data sends a packet having a preamble longer than this period. When the node recognizes the preamble during the LPL period, the node receives subsequent data. B-MAC also consumes energy.

The shortcomings of the conventional MAC protocol are as follows.

Energy Efficiency Aspects

S-MAC, which uses a fixed duty cycle, has better energy efficiency than traditional wireless MAC protocol, but performs unnecessary idle listening when the amount of data sensed by the node in the sensor network is extremely small. It is very inefficient.

To compensate for the problems in S-MAC, T-MAC adopts a flexible duty cycle, which saves energy by reducing the unnecessary idle listening time by operating a timer when the network traffic environment is low. By setting a separate timer, it consumes energy for that time. However, the duty cycle operation is impossible in an environment where the traffic of the network is very high, so that an efficient energy saving effect is hardly obtained.

S-MAC, T-MAC, and B-MAC not only consume energy to send data but also consume energy to send and receive control packets or long preambles, and also depending on the traffic environment. This is a waste of energy through idle listening. In addition, S-MAC and T-MAC consume additional energy by using CSMA-CA method, and B-MAC consumes additional energy due to overhearing.

<Network Latency Aspects>

The existing MAC protocol for sensor network has a very big disadvantage in network delay. S-MAC, T-MAC, and B-MAC protocols for sensor networks reduce the duty cycle to increase energy efficiency, and network delay increases proportionally. In other words, existing protocols maintain an inverse relationship with each other in terms of energy consumption and network delay. This causes problems when real-time applications are needed with limited power sources such as batteries. Especially when the network size of the sensor network is large, this delay causes a very big effect.

<High Priority Packet Processing Problem>

The use of wireless sensor networks for emergency monitoring requires the transmission of detected data at high priority. That is, when the data to be transmitted is urgent data, it should be transmitted preferentially to the non-urgent data, and a node having a high priority data should be given a transmission opportunity. However, the above-described conventional communication scheme does not suggest a method for giving priority to such transmission.

<Reliability Aspects>

Reliability has become an important requirement as sensor network technology is put into practical use. Reliability is the most important issue, especially when sensor network technology is applied to monitor emergency situations. The existing sensor network protocol only considers data transmission failure in terms of reliability. However, to ensure reliability, it is also necessary to monitor when the sensor node itself, which is responsible for the detection of a part of the entire monitoring area, fails or fails to operate.

In order to solve the above problems of the prior art, the present invention is to provide a protocol for a sensor network having a very small network delay through the synchronization between nodes in the low power communication method operating in a periodic Sleep / Active state .

It is another object of the present invention to provide a protocol for a low power sensor network by minimizing idle listening time in an active period in periodic sleep / active state operation.

Another object of the present invention is to provide a communication protocol having a linear structure.

It is yet another object of the present invention to provide an energy efficient mechanism for configuring and reconfiguring sensor network logical connections.

Hereinafter, the object of the present invention described above and other objects of the present invention and the configuration for implementing the same will be described in detail.

In the network configuration method of a sensor network for collecting and collecting sensed data from a plurality of sensors according to the present invention for achieving the above technical problem, all the sensor nodes except the sink node and the terminal node has its own upper node and lower node Linearly arranging communication paths of each node so that each node has one, and nodes included in the sensor network synchronize their time based on the operation interval of their upper node to synchronize the time of the entire network. There is provided a network configuration method of a sensor network comprising a.

According to another aspect of the present invention, the sensor data is collected and collected from a plurality of sensors, each node is a data transmission method of a sensor network having a serial linear communication path, a) each node in the sensor network Synchronizing its operation cycle according to the operation cycle of the upper node of b), b) any node in the sensor network receives data transmitted from its subnode in its reception cycle, c) said arbitrary A node of the node checks whether the transmission data is normal; and d) if the data is normal, transmitting the data to its higher node in its transmission period. This is provided.

According to still another aspect of the present invention, in a novel node joining method of a sensor network in which sensor data is collected and collected from a plurality of sensors, each node having a serial linear communication path, A terminal node periodically broadcasting a hello message indicating its presence, and a signal of the hello message received by the one or more sensor nodes wishing to join the sensor network. Calculating a link connection quality diagram from a state, the sensor node having the highest link connection quality diagram broadcasting a preemption message, and the sensor terminal broadcasting the preemption message in a transmission period, the current terminal. Sending a join message to the node, wherein the sensor node is configured to send the join message to the node. Current receive a confirmation message (ACK) for a message, there is provided a method his new node joining the network of sensors, comprising advertising that the new terminal node.

According to another aspect of the invention, the sensor collects and collects the sensing data from a plurality of sensors, each node has a series of linear communication paths, each node has its own unique network ID, the higher the node A method for relocating communication paths between nodes in a sensor network configured to have a low ID value, the method comprising: transitioning an arbitrary node that has received a transmission signal from its parent node but has not received an acknowledgment signal to the node; Transmitting a join message to a node having the smallest ID and a smallest ID value among its neighbor nodes, and when the receiving switch node receives the response message for the join message, transmits the response message. Node in the sensor network, including setting a node as its parent The communications path relocation method is provided.

In addition, as a sensor node for performing the method according to the features of the present invention described above,

A high priority buffer for temporarily storing emergency data, and a low priority buffer for temporarily storing general data, and first including the emergency data temporarily stored in the high priority buffer when generating a transport packet; When there is a redundancy in the data field of the transport packet, a sensor node is provided to include general data temporarily stored in the low priority buffer in the transport packet.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the configuration of the present invention.

<Real-time wireless sensor network protocol technology with linear structure (R-WSLP)>

The basic feature of the present invention is that the network is linear. Hereinafter, a wireless sensor network protocol having a real-time feature according to a feature of the present invention is referred to herein as a Real time-Wireless Sensor Line Protocol (R-WSLP).

The real-time wireless sensor network protocol technology having a linear structure of the present invention was created to ensure both low power and very low network delay in a large sensor network application environment. Was developed for. In particular, forest fire monitoring, safety monitoring of railroads, roads, piers, etc., and security facilities monitoring of defense, specific areas, buildings, etc., are important fields of real time, and this technology can be effectively applied.

The sensor network protocol according to the present invention utilizes a distributed TDMA based low duty cycle MAC algorithm and a time synchronized forwarding mechanism to transmit real-time sensing data and a large scale linear sensing field. Energy consumption is minimized by satisfying requirements such as efficient operation, low power consumption, elimination of overhearing, and minimization of control packet overhead. In addition, by simplifying the layer concept of the existing communication protocol, the control overhead is minimized through the integration of the link layer, network layer and transport layer. It also provides scalability through a self-organization function that automatically configures a virtual sensor line.

<Distributed TDMA>

The R-WSLP according to the present invention uses a distributed TDMA technique to ensure a low network delay while ensuring a low duty cycle for low power. Unlike conventional TDMA, distributed TDMA does not use a method in which a master node in a network allocates time slots of all nodes, and each node allocates its own time slot based on its parent. .

1 is a diagram illustrating a communication flow between nodes arranged linearly on a distributed TDMA basis. As shown in FIG. 1, each node is divided into an active period and an inactive period, and the active period receives data, transmits data, and receives ACK in the order of RX-TX-ACK. Between the nodes to be transmitted and received, the TX of the transmitting node and the RX of the receiving node are synchronized with each other through time synchronization to transmit and receive data. In fact, the time synchronization of the entire network is achieved by the time synchronization between the two nodes to transmit and receive data. In other words, all nodes of the network are synchronized with the node that exchanges data with themselves, and the entire network is distributed in synchronization.

2 is a diagram illustrating a manner in which network synchronization is performed in an R-WSLP according to the present invention.

From a network perspective, there is a CRP (Collision Resolution Period) in which nodes participate in communication while avoiding collisions based on TDMA, and Inter-CRP, which is a period of not using a communication channel used by the network. In R-WSLP, in order to avoid collision between nodes, the ICRP in the subnetwork composed of nodes within the communication distance based on the RF range of each node is set to be larger than the CRP.

For TDMA communication, each node performs time synchronization with its upper node. The accuracy of time synchronization in R-WSLP has a significant impact on network delay and power consumption. The time synchronization technique used in R-WSLP sets Timer_A which is responsible for periodic wake-up based on time stamp captured using the Start of Frame Delimiter (SFD) present in the packet sent by the upper node. If Timer_A disappears after a predetermined time, it performs its own RX-Data, TX-Data, and RX-Ack using Timer_B. Each node prevents the clock from shifting by resetting its Timer_A whenever it receives an SFD every RX-Ack period. In addition, a sufficient guard time is provided during transmission and reception to prevent the time synchronization from being broken by jitter. 2 shows a time synchronization method using two timers.

<Time Synchronized Forwarding Mechanism for Low Delay, Low Power Consumption>

One of the features of the present invention is a time-synchronized forwarding mechanism that achieves low delay, low power consumption based on the distributed TDMA described above. All nodes in the network operate on distributed TDMA based on the information of sink nodes. That is, all nodes repeat the periodic sleep and wakeup at the same period as the sink node. This period is time-synchronized with the immediate node in order to forward the data towards the sink node. 3 illustrates the basic concept of a time synchronized forwarding mechanism.

Node 1 performs time synchronization with its sink node, which is its parent node, and determines its wakeup period using the wakeup interval of the parent node. Node 2, the next node of Node 1, performs time synchronization with Node 1 and inherits the same wakeup interval. Nodes will then time synchronize with their parent nodes as well and inherit the same wakeup interval. Time-synchronized nodes operate in the order of RX-TX-ACK. Looking at the forwarding procedure based on Node 2 in the figure, it is as follows. Node 2 receives a message from Node 3 during its RX cycle. The Node 2 receiving the message forwards the message to the Node 1 node during the TX cycle by including the acquired sensing information and the information forwarded from the Node 3 in the message. Node 1 receiving the message checks whether the received message is useful by using FCS. If the message is successfully received, Node 1 makes a message using the detected information and data received from Node 2 and forwards it to the Sink node. At this time, Node 1 includes ACK information indicating that it correctly received data from Node 2 in its message by piggyback method. Node 2 listens to the message sent by Node 1 to the Sink node during its ACK cycle. If there is ACK information in the message received from Node 1 during the ACK cycle, Node 2 determines that the message has been successfully forwarded to Node 1, and in the case of a transmission error, it deletes the information put in the buffer for retransmission. This time-synchronized forwarding mechanism can greatly reduce the delay in which information collected from the sense node reaches the sink node in a low duty cycle environment.

The network delay from Node 3 to Sink node is T _{RX_Node1} + T _{RX_Node2} + T _{RX_Node3} + T _{RX_Sink} . That is, the network delay in R-WSLP is a value obtained by multiplying the number of transmission hops by the time taken to RX regardless of the duty cycle.

<Virtual track placement mechanism>

R-WSLP basically takes a linear topology. Linear topology has a form of having its own upper node and lower node, except for the sink node and the terminal node. A method of efficiently constructing such a linear topology according to the present invention will be described with reference to FIG. 4. 4 shows a virtual line arrangement mechanism.

The deployed wireless sensor nodes must be configured with a virtual line to match their physical location. In other words, the physically close nodes become their upper and lower nodes in the virtual line to become an efficient topology. When a node collecting data on a virtual line is called a sink node and the last node of the line is called a terminal node, the sink node becomes a terminal node at first, and the terminal node is a node most recently joined to the network while forming a virtual line. Will be. The terminal node periodically sends a Hello message or data to the parent node and uses this message to inform the child node that it is a terminal node. If there are several nodes around the terminal node, Link Quality Indication (LQI) is a method for measuring the physical distance so that the virtual line can be matched with the physical line as much as possible by joining in order from the nearest physical node among them. Use When a new node wants to join, it listens to the hello or data message of the current terminal node, and then receives the RSSI (Received Signal Strength Indicator) and the S-N ratio of the message received from the terminal node. To obtain the LQI. Nodes preempt join authority by sending a preemption message to neighboring nodes with the best LQI based on the measured values. The node sending the preemption message sends a join message the next time, and when it receives an ACK, it advertises itself as a new terminal node. Peripheral nodes that receive a preemption message are restricted from join attempts in the next wakeup period.

New nodes that want to join the network wait in RX On state to search for nearby Terminal nodes. In this state, when the terminal node receives a message, it synchronizes time and measures the LQI. Nodes that receive a message from the terminal send a preemption message based on the measured LQI. These preemption messages are adjusted so that nodes with good LQI values are sent first, and nodes with similar values avoid collisions through random backoff. The neighboring nodes receiving the preemption message will postpone the joining procedure until the next cycle. This series of procedures allows the terminal node and the node whose LQI is determined to be the best among the nodes to join to join first. That is, the virtual line arrangement is achieved through this procedure. In this case, the start of the interval where the node can send preemption is limited after T / 2 in order to avoid collision by sending a message after the CRP interval of the upper nodes of the terminal node.

Nodes set their network ID to one greater than their parent node's network ID upon initial join. This value will be maintained until the network is reset.

<Virtual track relocation mechanism>

Virtual Line Rearrangement Mechanism for Self Healing of Sensor Network is used to reconfigure the Virtual Line to reconfigure the Virtual Line when the upper node malfunctions or does not communicate from the Virtual Line to the Sync Node. Autonomously connect with. Figure 5 illustrates the Virtual Line Rearrangement Mechanism.

If node 4 does not receive an ACK message from node 3 more than three times, node 4 is changed to RX On and joins the parent node in a similar procedure to Virtual Line Arrangement Mechanism. At this time, if node 2, which is the upper node of node 3, identifies a problem of node 3, which is its lower node, it may recognize itself as a terminal node and broadcast a hello message to reposition the path based on the aforementioned Virtual Line Arrangement Mechanism. Alternatively, if node 2 does not recognize the problem of node 3, node 2 will not broadcast the hello message, so that node 4, which has recognized the problem of node 3, has the same value as its own node and its ID value. When a small but small difference is transmitted, a join message destined for the node 2 is transmitted, and when a response message for the join message is received from the node 2, the node 2 is set as its parent. You can relocate.

Node 4 attempts to connect to a node having a smaller network ID than the node among nodes recognized as adjacent nodes and having the smallest difference in ID to form a new virtual line. There is no change in Network ID during the rearrangement process.

<High Reliability Data Transfer>

R-WSLP according to the present invention uses a piggyback acknowledgment method to ensure reliable data transmission and network reliability, virtual node relocation for error node monitoring, network self-healing It provides the function of the Virtual Line Rearrangement Mechanism.

First, the piggyback acknowledgment method is sent by including an ACK for the opposite direction in the message sending data in the sink direction. In other words, by sending one message, it acts as a data message in the sink direction and as an ACK message in the terminal direction, thereby eliminating the need for a separate control message for the ACK. If the lower node does not receive the ACK correctly, it will retransmit the next cycle. In addition, if a node does not receive a message in the next cycle from a subordinate node connected to itself for monitoring the node where an error occurred, an error is reported to the sink node by using the network ID of the node. The server monitors the failed node in real time and this information is stored in the database.

<Data Clustering Transfer>

In the R-WSLP according to the present invention, a transmission method through data aggregation is used. The method of sending several bytes of sensor data one by one causes not only the overhead incurred by the header of the packet but also a lot of computing demands on the system and a large processing time in order to process the same. In R-WSLP, this problem was solved using data aggregation. 6 shows a packet structure for data aggregation.

Payload in R-WSLP packet consists of a set of sub-payload. Sub-payload is composed of a SourceID indicating the ID of the node from which data is collected, a DataType field indicating a type of sensing data, and a Data field for loading actual data. In particular, the DataType field serves as a reference for monitoring and control packets, as well as for emergency data, and whether a DataType field is 1 byte or 2 bytes.

<Emergency Data Priority Transmission Policy through Packet Priority>

The R-WSLP of the present invention is designed for an environment in which low data traffic occurs. However, under special circumstances, a large amount of network traffic may occur instantaneously. In this situation, priority can be given to the data to guarantee the priority transmission of emergency data.

Each sensor node has two ring buffers, High Priority Buffer and Low Priority Buffer, and the data received from the lower node or the data obtained from its own sensor is marked in the Data Type field according to the priority and the corresponding priority. Write to the buffer. For data transmission, the sub-payload is first taken from the high priority buffer within the MTU (Maximum Transmission Unit) size that can be sent to the payload of the corresponding period, and the sub-payload having the low priority is loaded in the remaining space.

Although the configuration of the present invention has been described in detail with reference to the accompanying drawings, the scope of the present invention is not limited thereto, and a person skilled in the art may have various modifications without departing from the spirit of the present invention. And changes will be possible. Therefore, the protection scope of this invention is defined by description of the following claims.

As described above, according to the present invention, it is possible to reliably transmit data with low transmission delay while reducing power consumption of each node of the sensor network, and to implement a real-time sensor network capable of processing emergency data that requires rapid processing. have.

Claims (11)

In the network configuration method of a sensor network for collecting and collecting sensed data from a plurality of sensors, Linearly arranging communication paths of each node such that all sensor nodes except the sink node and the terminal node have their own parent node and one child node; Nodes included in the sensor network adjust the time synchronization of the entire network based on their time synchronization based on the operation interval of their parent node Network configuration method of the sensor network comprising a. The method of claim 1, a) synchronizing the time, synchronizing the two nodes by synchronizing the transmission interval of the lower node immediately following the reception interval of the highest sync node; b) synchronizing the subnode below it by the subnode immediately below it; c) repeating step b) to achieve time synchronization of the entire network Network configuration method comprising a. The method of claim 1, Wherein each node is allocated a transmit / receive time in a time division access manner. In the data transmission method of the sensor network collecting and collecting sensed data from a plurality of sensors, each node having a serial linear communication path, a) each node in the sensor network synchronizes its operation cycle according to its parent node's operation cycle, b) any node in the sensor network receiving data transmitted from its subnodes in its reception period, c) the arbitrary node checking whether the transmission data is normal; d) if the data is normal, any node transmits the data to its parent node in its transmission period Data transmission method comprising a. The method of claim 4, wherein step d) Generating a transport packet comprising data from the subnode and / or data detected by the node; Inserting an ACK signal into the transport packet; Simultaneously transmitting the transport packet to the upper node and the lower node Data transmission method comprising a. The method of claim 5, If any node in the sensor network does not receive the transport packet from its parent node, it retransmits it in the next transmission cycle.If the node receives the transport packet, it determines that the transmission to its parent node is completed and the data in its buffer Canceling the data transmission method. The method of claim 5, The transport packet includes an identifier of a node that senses data, a data type identifier indicating a type of data, and sensed data. In the new node joining method of the sensor network collecting and collecting sensed data from a plurality of sensors, each node having a serial linear communication path, A terminal node at the end of the linear structure sensor network periodically broadcasting a hello message indicating its presence; Calculating, by one or more sensor nodes intending to join the sensor network, a link connection quality diagram from the signal state of the hello message received to the sensor network; A step in which the sensor node having the highest link connection quality broadcasts a preemption message; Transmitting, by the sensor node, a join message to the current terminal node in a transmission period after the preemption message is broadcast; When the sensor node receives an acknowledgment message (ACK) for the joining message, advertising that it has become a new terminal node. Joining a new node of the sensor network comprising a. The method of claim 8, wherein the broadcasting of the preemption message comprises: Broadcasting the preemption message at a faster time point as the sensor node having a higher degree of the calculated link connection quality; And deferring new joins by neighboring nodes upon receiving the preemption message. Collecting and collecting sensed data from multiple sensors, each node has a series of linear communication paths, and each node has its own unique network ID, but the node of the sensor network whose parent node has less ID value In a method for relocating communication paths, Transitioning to a standby state by an arbitrary node that transmits from its parent node but does not receive an acknowledgment signal from it; Transmitting, by the reception switching node, a joining message to a node having a smallest difference between itself and an ID value among neighboring nodes; When the receiving standby switching node receives the response message for the joining message, setting the node that sent the response message as its parent node; Node-to-node communication path relocation method of the sensor network comprising a. A sensor node for performing the method of any one of claims 1 to 10, A high priority buffer for temporarily storing emergency data, Includes a low priority buffer to temporarily store regular data, When generating a transport packet, the emergency data temporarily stored in the high priority buffer is first included, and when the data field of the transport packet is redundant, general data temporarily stored in the low priority buffer is included in the transport packet. Sensor node.

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